Selective application of conductive material to circuit boards by pick and place

ABSTRACT

A component for use in manufacturing circuit boards, such as printed circuit boards, or flex substrates is adapted for use with pick-and-place equipment to provide a first material overlay disposed over a second material base layer. Such a component may include a first electrically conductive material disposed over a second electrically conductive material, and a soluble tape backing disposed over and attached to the second electrically conductive material. The component may be attached to a circuit board by solder relow, after which the soluble tape backing is removed. Although typical embodiments involve electrically conductive materials, it is noted that an electrically insulating material can also be disposed over and attached to an underlying material which itself is disposed on a circuit board.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of earlier filed provisionalApplication No. 60/494,710, filed 12 Aug. 2003, and entitled “SelectiveApplication Of Conductive Material To Circuit Boards By Pick And Place”.

FIELD OF THE INVENTION

The present invention relates generally to electronic productmanufacturing, and more particularly relates to the application ofconductive material to selected areas of a circuit substrate, such as aboard, by pick and place operations.

BACKGROUND

Many electronic products are provided in the form of a plurality ofcomponents, such as, electrical circuit elements and/or integratedcircuits, mounted upon an underlying substrate, wherein that substrateprovides various conductive paths between two or more of the mountedcomponents, and/or between at least one of the mounted components and anexternal connection terminal. One well known form of substrate formounting components and for providing the aforementioned conductivepaths is the printed circuit board.

Printed circuit board manufacturing generally involves the formation ofa plurality of conductive traces disposed on at least one major surfaceof a generally planar, generally rigid, insulating material. Manyinsulating materials have been used to form substrates for electronicproducts, such as, but not limited to, FR4, epoxy, and ceramics. Printedcircuit boards may have conductive traces disposed on each of twoopposing sides thereof. Similarly, printed circuit boards may have oneor more layers of conductive traces disposed within the insulatingmaterial. Printed circuit boards may have holes, or openings,therethrough for the mounting of components, mechanical alignment of theprinted circuit board to another unit, or plated through holes for theinterconnection of the various layers of conductive traces.

A substrate similar to the printed circuit board, but which is notgenerally rigid, is referred to herein as a flex substrate. Such flexmaterials with patterned conductive traces are well known in theelectronic arts and have been used for a variety of applicationsincluding backplane connector cables, and for providing a base uponwhich components may be attached.

A common manufacturing process for forming conductive traces on printedcircuit boards, includes forming a blanket layer of conductive materialand then etching away certain portions so as to form spaces between theremaining conductive material which, subsequent to this etchingoperation, is in the form of conductive traces. A commonly usedconductive material for such applications is copper.

In certain circumstances, conductive material with chemical andelectrical properties different from those of copper are required. Oneconductive material that is used in such circumstances is gold. Gold hasa lower electrical resistivity than copper, and this lower electricalresistivity provides for improved electrical performance in many typesof electrical circuits. Additionally, gold, as compared to copper, hasthe desirable property of being less reactive to atmospheric gases, andhence is less likely to corrode.

Those skilled in the electronic arts in general, and in circuit boarddesign and manufacturing; and integrated circuit packaging, sinparticular, will recognize that although gold has certain desirableelectrical and chemical properties, it is an expensive element toinclude in a product or in a manufacturing process. In addition to beingexpensive, some manufacturing processes for applying gold require a wetchemical environment.

What is needed are methods and apparatus that are convenient andcost-effective for applying gold to portions of substrates, such as,circuit boards and integrated circuit packages.

SUMMARY OF THE INVENTION

Briefly, application of a conductive material onto selected pads of acircuit board, includes forming one or more conductive pad structures,or padstacks, by patterning a sheet that includes a stack of materiallayers. Such conductive pad structures may include a first conductivetop layer, one or more underlying layers, and a bottom attachment layer,such as, a solder layer. The-top layer of one or-more padstacks areadhered to a soluble tape, and this composite structure is moved intoplace over a selected region of a substrate by means of a pick-and-placeoperation.

In a further aspect of the present invention, the placement of padstacksis followed by a solder reflow operation by which the padstacks areadhered to contact pads of the substrate.

In a still further aspect of the present invention, a wash with asolvent suitable to remove the soluble tape is performed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a gold pad structure with solder on the bottomthereof in accordance with the present invention.

FIG. 2 is a cross-sectional view of a gold pad in accordance with thepresent invention, illustrating various layers of conductive material ofthe structure including a gold layer, a nickel layer subjacent the goldlayer, a copper layer subjacent the nickel layer, and a solder layersubjacent the copper layer.

FIG. 3 illustrates a water soluble tape with a plurality of patternedgold pad structures disposed thereon, such that the solder layer isexposed and the gold layer is in contact with the water soluble tape.

FIG. 4 is a top view of a patterned layer of gold pad structuresillustrating that the gold pad structures may have a wide variety ofshapes and sizes.

FIG. 5 is a side view of an illustrative multi-layer printed circuitboard with solder paste disposed on a plurality of pads; and apick-and-place mechanism holding a gold pad structure/soluble tapecombination aligned above the printed circuit board for placementthereon.

FIG. 6 shows the structure of FIG. 5 after the gold padstructure/soluble tape combination has undergone a solder reflowoperation.

FIG. 7 shows the structure of FIG. 6 after the soluble tape has beendissolved in a wash cycle.

FIG. 8 shows a top view of an unpatterned stack of materials having goldas the top layer.

FIG. 9 shows the structure of FIG. 8 after both “field”, and “gold pad”structures (i.e., padstacks) have been defined by way of a lasercutting, or etching, operation.

FIG. 10 is a cross-sectional view of an unpatterned stack of materialssimilar to that shown in FIG. 2, except the attachment layer iscomprised of either flux, solder paste, or conductive ink.

FIG. 11 is a cross-sectional view of the structure of FIG. 9, whereinthe structure is disposed upon a fixture such as, for example, a vacuumhold down.

FIG. 12 is a cross-sectional view of the structure of FIG. 11, whichalso shows a water soluble tape being applied by a pressure roller.

FIG. 13 is a cross-sectional view of a pick-and-place footprint for agold pad structure in accordance with the present invention.

FIG. 14 is a cross-sectional view of the gold pad structure of FIG. 13,after that structure has been placed onto a substrate, such as, forexample, a printed circuit board having a solder mask thereon.

FIG. 15 is a flow diagram illustrating a method of making a structure inaccordance with the present invention.

FIG. 16 is a flow diagram illustrating a method of making a structure inaccordance with the present invention.

DETAILED DESCRIPTION

Various embodiments of the present invention provide a new class ofcomponent for use in manufacturing electronic products including printedcircuit boards, flex substrates, or integrated circuit packaging. Moreparticularly, various embodiments of the present inventionprovide-pick-and place operations to provide a first material overlaydisposed over a second material base layer.

In typical embodiments of the present invention, a first electricallyconductive material is disposed over a second electrically conductivematerial and attached thereto. Although typical embodiments involveelectrically conductive materials, it is noted that an electricallyinsulating material could also be disposed over, and attached to, anunderlying material which itself is disposed on a substrate such as, forexample, a circuit board.

Specific embodiments of the present invention provide for putting goldon pads of printed circuit boards, away from the edges of such printedcircuit boards. Such selective application of gold by pick-and-placeoperations followed by a solder reflow, and wash cycle, provide forconvenient and cost-effective creation of gold-plated contact pads oncircuit boards.

Reference herein to “one embodiment”, “an embodiment”, or similarformulations, means that a particular feature, structure, operation, orcharacteristic described in connection with the embodiment, is includedin at least one embodiment of the present invention. Thus, theappearances of such phrases or formulations herein are not necessarilyall referring to the same embodiment. Furthermore, various particularfeatures, structures, operations, or characteristics may be combined inany suitable manner in one or more embodiments.

Reference herein to “circuit boards”, unless otherwise noted, isintended to include any type of substrate upon which a material may beselectively placed. For example, such substrates may be rigid orflexible, ceramic, flex, epoxy, FR4, or any other suitable material.

As noted above, some electrical or electronic products require a highlyconductive material, such as gold, to be put on the pads of printedcircuit boards. Conventionally, putting gold on pads of printed circuitboards that are located away from the edges of those boards can add 15%to 20% to the cost of each such board. Gold pads are often required fornon-soldered, pressure connect mounting of land grid array (LGA)packages into sockets.

In one aspect of the present invention, a component is provided to more.conveniently, efficiently, and cost-effectively provide for theapplication of a highly electrically conductive material, such as gold,onto a plurality of pads disposed on a board, such as a printed circuitboard. Such a component may be referred to as a gold pad array, or mayalternatively be referred to as a padstack.

FIG. 1 illustrates a gold pad structure 100 in accordance with thepresent invention, that has gold on a first surface and solder on anopposing surface thereof. It is noted that although gold is a presentlypreferred material, the present invention is not limited to the use ofgold, and that any material with the desired electrical, chemical,and/or physical properties may be used in conjunction with the presentinvention.

FIG. 2 is a cross-sectional view of gold pad structure 100, illustratingvarious layers of conductive material of the structure including a goldlayer, a nickel layer subjacent the gold layer, a copper layer subjacentthe nickel layer, and a solder layer subjacent the copper layer. Thecopper layer may be referred to as a base layer. Gold pad structure 100may be formed such that a material other than copper is selected as thebase layer, for example, brass, or other metallic alloys; conductiveplastic (intrinsic or filled with conductive particles); metallizedorganic fibers (random or woven); metallized perforated organic sheet;metallized perforated inorganic sheet; perforated organic sheet withconductive hole filler; or perforated inorganic sheet (with conductivehole filler) may be used. The solder layer may be disposed subjacent thecopper layer of gold pad structure 100 by any suitable means, includingbut not limited to Sputtering; electroplating; electroless plating;printing (stencil/screen); evaporating; dipping; laminating sheet stock.The solder layer is used as an attachment layer, typically for attachinga padstack to pads on a substrate such as a printed circuit board. Theattachment layer may alternatively be formed from materials such as, butnot limited to, flux, solder paste, or conductive ink.

FIG. 3 illustrates a water soluble tape with a plurality of patternedgold pad structures 100 disposed thereon, such that the solder layer isexposed and the gold layer is in contact with the water soluble tape. Inone embodiment of the present invention, the metal stack structure shownin FIG. 2 is formed on a tape backing and patterned to form individualgold pad structures 100. As illustrated in FIG. 3, the gold layer isadjacent the water soluble tape and the solder layer is exposed. Thisgold pad structure/soluble tape combination is used in accordance withmethods of the present invention to provide gold-plated pads on circuitboards.

The water soluble tape is typically a poly-vinyl alcohol with syntheticwater soluble adhesive. Such a water soluble tape is the Water-SolubleWave Solder Tape—5414 available from 3M Corp.

FIG. 4 is a top view of a patterned layer of gold pad structures 100illustrating that gold pad structures 100 may have a wide variety ofshapes and sizes. The present invention is not limited to any particularshape or size of gold pad structures 100.

FIG. 5 is a side view of an illustrative multi-layer printed circuitboard with solder paste disposed on a plurality of pads; and a pick andplace mechanism holding a gold pad structure/soluble tape combinationaligned above the printed circuit board for placement thereon. Thesoluble tape is preferably soluble in a solvent such as water, but thepresent invention is not limited to any particular solvent.

FIG. 6 shows the structure of FIG. 5 after the gold padstructure/soluble tape combination has undergone a solder reflowoperation. The solder reflow operation serves to attach the gold padstructure/soluble tape combination to the underlying circuit board. Thesoluble tape backing provides mechanical support of the gold padstructures 100 until the solder reflow operation attaches the gold padstructures 100 to the circuit board.

FIG. 7 shows the structure of FIG. 6 after the soluble tape has beendissolved in a wash cycle. It can be seen that after the tape has beendissolved, the gold surface of gold pad structures 100 are present onthe surface of the selected portions of the circuit board where the pickand place operation had disposed the gold pad structure/soluble tapecombination

FIG. 8 shows a top view of an unpatterned stack of materials having goldas the top layer. In this illustrative embodiment, the stack has a toplayer of gold, a nickel layer subjacent the gold layer, a copper layersubjacent the nickel layer and a solder layer subjacent the copperlayer. It is noted that various embodiments of the present invention mayuse any suitable alternative material stacks.

FIG. 9 shows the structure of FIG. 8 after both field, and gold padstructures (i.e., padstacks) have been defined, or patterned, by way ofa laser cutting, or etching, operation. In typical embodiments of thepresent invention, lasers in the near infra-red, green, or ultravioletwavelengths may be used. Patterning may alternatively be accomplished bymeans of, for example, a water-jet with abrasive content; laser energydelivered with a water-jet; a saw; a die cutter; an ion beam (nottypically used for other than very small patterns); or an air drivenabrasive stream.

With respect to the patterning operations described above, it is notedthat laser etching may be performed from either the top side (i.e.,gold-side in this example) or from the bottom side (i.e., thesolder-side in this example).

FIG. 10 is a cross-sectional view of an unpatterned stack of materialssimilar to that shown in FIG. 2, except the attachment layer iscomprised of either flux, solder paste, or conductive ink.

FIG. 11 is a cross-sectional view of the structure of FIG. 9, whereinthe structure is disposed upon a fixture such as, for example, a vacuumhold-down fixture. FIG. 12 is a cross-sectional view of the structure ofFIG. 11, which also shows a water soluble tape being applied by apressure roller.

Referring to FIGS. 11-12, the unpatterned stack is placed solder-sidedown on a hold-down fixture, such as for example, a vacuum plate, or avacuum chuck. The laser etching operation is then performed. A watersoluble sticky tape is then applied to the surface of the patternedstack of materials, in this example by means of rollers. The padstacksare lifted away from the field portion of the material stack by thewater soluble sticky tape It is noted that although a water solublesticky tape is used in this example the invention is not limited totapes that are water soluble.

In an alternative embodiment,

FIG. 13 is a cross-sectional view of a pick-and-place footprint for agold pad structure in accordance with the present invention.

FIG. 14 is a cross-sectional view of the gold pad structure of FIG. 13,after that structure has been placed onto a substrate, such as, forexample, a printed circuit board having a solder mask thereon.

FIG. 15 is a flow diagram illustrating a method of making a structure inaccordance with the present invention. In this illustrative embodiment,a base layer having a first major surface and a second major surface isprovided 1502. The base layer is typically a sheet of metal. In variousembodiments a cleaning operation may be performed on the base layer toremove, for example, oxidation or other contaminants. A first layer ofmaterial is disposed 1504 over the first surface of the base layer. Invarious embodiments, there may be one or more intervening materiallayers disposed between the base layer and the first layer. Anattachment layer is disposed 1506 adjacent the second major surface ofthe base layer.

FIG. 16 is a flow diagram illustrating a method of making a padstackstructure in accordance with the present invention. In this illustrativeembodiment, a copper base layer is provided and cleaned 1602. A firstmasking layer is then disposed 1604 over a bottom surface of the baselayer. It will be appreciated that references to “top” and “bottom”surfaces are for the convenience of description, and are not intended tobe limitations on the particular spatial orientation structures inaccordance with the present invention. The top surface of the baselayer, which is not masked, is then plated 1606 with nickel. The nickellayer is then plated 1608 with gold to form a gold layer. The firstmasking layer is then removed 1610. A second masking layer is disposed1612 over the gold layer. A solder layer is disposed 1614 over thebottom surface of the base layer. The second masking layer is thenremoved 1616. The gold, nickel, copper and solder layers are then laseretched 1618 to form isolated padstacks.

In typical embodiments, a padstack provides an electrically conductivepathway between its top and bottom surfaces. It is noted thatalternative padstacks may include one or more layers that are notelectrically conductive, such that an electrical pathway does not existbetween the top and bottom surfaces of the padstack.

CONCLUSION

Various embodiments of the present invention include apparatus andmethods for selectively applying a material to portions of a circuitboard. More particularly, various embodiments of the present inventionprovide a structure suitable for use with existing pick-and-placeequipment that can be placed on, and adhered to, a circuit board, andsubsequently have an unneeded tape portion dissolved away.

Embodiments of the present invention may find application in themanufacture of in various electronic or opto-electronic products thatinclude printed circuit boards, flex substrates, ceramic substrates, orsimilar elements.

An advantage of some embodiments of the present invention includes thecost-effective selective application of material, such as, for example,gold, to circuit boards.

Another advantage of some embodiments of the present invention includesthe ability to use conventional pick-and-place tools to providegold-plating for selective portions of circuit boards.

A still further advantage of some embodiments of the present inventionincludes selectively disposing gold contact regions on a circuit boardwithout exposing the circuit board to wet chemical processing.

It is to be understood that the present invention is not limited to theembodiments described above, but encompasses any and all embodimentswithin the scope of the subjoined Claims and their equivalents.

1. A structure for use in applying conductive materials to a portion ofa circuit board, comprising: a first conductive layer; a secondconductive layer disposed over, and attached to, the first conductivelayer; a third conductive layer disposed over, and attached to, thesecond conductive layer; a fourth conductive layer disposed over, andattached to, the third conductive layer; and a soluble tape disposedover, and attached to, the fourth conductive layer.
 2. The structure ofclaim 1, wherein the structure is adapted for use with a pick and placeprocess.
 3. The structure of claim 2, wherein the first conductive layercomprises solder, the second conductive layer comprises copper, thethird conductive layer comprises nickel, and the fourth conductive layercomprises gold.
 4. The structure of claim 3, wherein the soluble tape isa water soluble tape.
 5. The structure of claim 3, wherein the solubletape is formed of a material that does not decompose while within adistance of a solder reflow operation, and that distance is equal to thesum of the thicknesses of the first, second, third, and fourthconductive layers.
 6. A method of selectively applying a conductivematerial to a circuit board, comprising: providing circuit board havingpatterned electrically conductive material thereon; picking a platingcomponent and placing the plating component on a selected portion of thepatterned electrically conductive material of the circuit board; andattaching the plating component to the selected portion of the patternedelectrically conductive material of the circuit board.
 7. The method ofclaim 6, wherein the plating component comprises a first conductivelayer, a second conductive layer disposed over, and attached to, thefirst conductive layer, a third conductive layer disposed over, andattached to, the second conductive layer, a fourth conductive layerdisposed over, and attached to, the third conductive layer, and asoluble tape disposed over, and attached to, the fourth conductivelayer.
 8. The method of claim 6, wherein the plating component comprisesat least a first conductive layer, a second conductive layer disposedover the first conductive layer, and a soluble backing layer disposedover and attached to the second conductive layer.
 9. The method of claim8, wherein the first conductive layer comprises solder and the secondconductive layer comprises gold.
 10. The method of claim 8, whereinattaching the plating component comprises a solder reflow operation. 11.The method of claim 10, further comprising removing the soluble backinglayer.
 12. The method of claim 11, wherein removing the soluble backinglayer comprises washing with water.
 13. A method of making a padstacks,comprising: cleaning a copper base layer having a first and a secondmajor surface; disposing a first mask layer of the second major surfaceof the base layer; plating a layer of nickel over the first majorsurface of base layer; plating a layer of gold over the layer of nickel;removing the first masking layer from the second major surface of thebase layer; disposing a second masking layer over of the gold layer;disposing an attachment layer adjacent the second major surface of thebase layer, thereby forming a material stack including gold, nickel,copper and attachment layers; removing the second masking layer fromover the gold layer; laser etching the gold, nickel, copper, andattachment layers to isolate padstacks from the gold, nickel, copper,and attachment layers.
 14. The method of claim 13, wherein theattachment layer is a solder layer.
 15. The method of claim 13, whereinthe attachment layer is a solder paste.
 16. The method of claim 13,wherein the attachment layer is a conductive adhesive.
 17. The method ofclaim 13, further comprising, prior to laser etching, disposing thematerial stack on a vacuum hold-down fixture, such that the attachmentlayer is adjacent the vacuum hold-down fixture.
 18. The method of claim17, wherein laser etching comprises directing laser energy of apredetermined wavelength at the material stack from the gold layer side;and further comprising, subsequent to laser etching, applying a solublesticky tape adjacent to the gold layer of the laser etched materialstack.
 19. The method of claim 13, further comprising, prior to laseretching, applying a water soluble tape to the gold layer of the materialstack.
 20. The method of claim 19, wherein laser etching comprisesdirecting laser energy of a predetermined wavelength at the materialstack from the attachment layer side, and wherein the water soluble tapeis substantially transparent to the laser energy of the predeterminedwavelength.